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ST LOUIS, MISSOURI – AUGUST 8: Riley O’Brien #55 of the St. Louis Cardinals pitches against the Chicago Cubs in the ninth inning at Busch Stadium on August 8, 2025 in St Louis, Missouri. (Photo by Joe Puetz/Getty Images)

A calf injury has slowed St. Louis Cardinals right-hander Riley O’Brien since the start of spring training. The delay has thrown doubt into the Cardinals‘ closer situation at the start of the season, but it will also keep the 31-year-old from participating in the World Baseball Classic next month for Team Korea.

O’Brien’s injury occurred during a bullpen session on Saturday, according to MLB.com’s Chuck King. He hasn’t thrown off a mound since.

Team Korea Will Need to Shift Gears

There was a lot of excitement within Team Korea surrounding this year’s WBC roster. The team included a non-Korean-born player for the first time during the last World Baseball Classic tournament, with Tommy Edman joining the roster. Edman was eligible because his mother was born in South Korea.

While Edman won’t be joining the team again this year following October surgery, Korea was anticipating the inclusion of two other players: O’Brien and Tigers utilityman Jahmai Jones. Both players are eligible because their mothers were born are Korean. O’Brien was believed to be a favorite to serve as the team’s closer.

Team Korea has added Doosan Bears right-hander Taek Yeon Kim to replace O’Brien on the roster. The 20-year-old has collected 43 saves while posting a 2.81 ERA with 157 SO in 131.1 IP over his two seasons in the KBO.

South Korea will play Japan, Australia, Chinese Taipei, and Czechia in Pool C. Those games will be played in Japan’s Tokyo Dome, beginning on March 5.

The Cardinals Have Options if Riley O’Brien Misses Significant Time

In addition to being the favorite to close out games for Team Korea, O’Brien entered camp as the projected closer for the Cardinals. If the calf injury forces him to miss any time during the regular season (or even depending on how much of spring training he’s behind the other relievers), it could force the team to shift gears regarding how manager Oliver Marmol handles the late innings.

Left-hander JoJo Romero will presumably get the first crack at the closer role, providing he isn’t traded before the end of spring training. The 29-year-old had the best season of his career in 2025, posting a 2.07 ERA in 61.0 IP while collecting eight saves.

Right-handers Ryne Stanek and Matt Svanson have also been identified as potential candidates for the ninth inning. The veteran Stanek, 34, has far more experience, having pitched for five teams over a nine-year career, not to mention his postseason pedigree (a 2.89 ERA over 28.0 IP), working in his favor. Svanson, 27, made his debut last season for the Cardinals, pitching to a 1.94 ERA over 60.1 IP.

Aaron Somers Aaron Somers has been writing about baseball on a global scale since the early 2000’s. His content has appeared at several outlets over those years, with most of his recent words coming at his To Be Named Later newsletter. More about Aaron Somers

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